Before consignment of radioactively contaminated material to a waste disposal site, for example, a waste landfill site, it must be ensured that the contamination of the material is below the specified disposal limits of the site. It is therefore often necessary to treat the contaminated materials before disposal in order to ensure that the contamination levels are within the disposal limits.
Products, for example gloves and sheets, made of plastics material are widely used in the processing and handling of radioactive material. Difficulties have been experienced in cleaning such material sufficiently to enable it to be disposed of safely.
Attempts to clean contaminated plastics material by simply subjecting the material to a nitric acid leaching operation, followed by at least one washing cycle have proved to be unsatisfactory. It was found that the material had not been cleaned sufficiently to enable safe disposal.
A known process for cleaning contaminated waste plastics material is described in International Publication No. 95/16997. This process comprises washing the material in water which contains a strong base, such as soda or potash in aqueous solution. Optionally, a wetting agent, preferably non-foaming, may also be added to the water. During the washing operation a saponification reaction occurs so that the material is subjected to a selective chemical treatment whereby certain surface agents, for example, plasticisers, which contain most of the contaminants are attacked. The washed material is then rinsed in water.
A disadvantage of this process is that the contaminants, such as uranic substances, are not rendered soluble and this presents certain difficulties in their recovery. Recovery must be effected by a solid-liquid separation process, such as filtration, followed by either direct leaching of the uranic substances from the filter, or by physical removal of the solids from the filter and then leaching the uranic substances from the removed solids.
It is an object of the present invention to provide a method of cleaning radioactively contaminated plastics material which is efficient and enables the treated material to be disposed of safely.